How to search in Mail.app within Gmail Chat history?

Zevlag is right. You're not going to be able to do precisely what you were after (true IMAP syncing of chat logs). But here's a couple of things that you can:

First, you could download your chat logs using this method: http://freshhorse.wordpress.com/2011/07/29/leaving-gmail-and-bringing-your-chats-with-you/

• This will take quite a bit of time and I doubt you'd want to do it over and over to keep your logs up-to-date. But it will allow you to have an easily searchable record of your chats on your local machine (Spotlight).

Second you could look into Google's APIs for a way to get at your chats. Here's one example of a script attempting this:

https://gist.github.com/1051628

• This will be even more complicated and still won't get you what you're after but if your a bit of a hacker you might be able to put something together with the API that would keep your local record up-to-date.

Sorry there isn't a way to do just what you want.

-Samuel